1. Field of the Invention
The present invention relates to a matrix-type liquid crystal display device.
2. Description of the Related Art
As regards the display device used, for example, as a monitor for OA devices such as word processor, notebook computer and personal computer, as well as in a mobile device or a television, CRT (cathode ray tube) has been heretofore mainly used. In recent years, a liquid crystal display is becoming widely used instead of CRT because of its small thickness, light weight and low power consumption. The liquid crystal display device comprises a liquid crystal cell and a polarizing plate. The polarizing plate is usually composed of a protective film and a polarizing film and is obtained by dyeing a polarizing film comprising a polyvinyl alcohol film with iodine, stretching the film and stacking a protective film on both surfaces of the film. In a transmission-type liquid crystal display device, this polarizing plate is fixed on both sides of a liquid crystal cell and in some cases, one or more optically compensatory sheets are further disposed. In a reflection-type liquid crystal display device, there are usually disposed a reflector plate, a liquid crystal cell, one or more optically compensatory sheets and a polarizing plate in this order. The liquid crystal cell usually comprises a liquid crystal molecule, two substrates for encapsulating the liquid crystal molecule, and an electrode layer for applying a voltage to the liquid crystal molecule. The liquid crystal cell displays an ON or OFF mode depending on the difference in the aligned state of liquid crystal molecules and can be applied to all of transmission-type, reflection-type and transflection-type display devices. Display modes such as TN (twisted nematic), IPS (in-plane switching), OCB (optically compensatory bend), VA (vertically aligned), ECB (electrically controlled birefringence), and STN (super twisted nematic) have been proposed.
The optically compensatory sheet is used in various liquid crystal display devices for eliminating the image coloration or enlarging the viewing angle. As for the optically compensatory sheet, a stretched birefringent polymer film has been conventionally used. Instead of the optically compensatory sheet comprising a stretched birefringent film, it is proposed to use an optically compensatory sheet comprising a transparent support having thereon an optically anisotropic layer formed of a low or high molecular liquid crystalline compound. The liquid crystalline compound has various orientation modes and therefore, by using a liquid crystalline compound, an optical property unobtainable by conventional stretched birefringent polymer films can be realized. Furthermore, this optically compensatory sheet functions also as a polarizing plate protective film.
On the other hand, in an image display device such as CRT, plasma display panel (PDP), electroluminescent display (ELD), field emission display (FED), surface-conduction electron-emitter display (SED) and liquid crystal display device (LCD), the display performance in a bright-room environment can be enhanced by preventing the display surface from a disturbing image reflection due to reflection of outside light.
As for the method of preventing a disturbing image reflection on the display surface of an image display device, there are disclosed (1) a method where a performance of blurring the contour of the disturbing reflection image by the effect of surface scattering (antiglare property) is imparted to make less recognizable the disturbing reflection image, and (2) a method where a performance of reducing the amount of reflected light (antireflection property) is imparted by providing a low refractive index layer on the outermost surface of the display surface and the disturbing reflection image is thereby made less recognizable (see, Japanese Patent No. 3,507,719 and JP-A-2003-270409 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)).
In recent years, the market for applications using a display device with a large screen and allowing a user to watch a high-quality moving picture from a relatively distant position as typified, for example, by a liquid crystal television is rapidly expanding. In such an application, the display is required to show a clearer image. In the case where the antiglare property is strong, when a thing, a fluorescent lamp, a human being or the like located in the periphery of the display casts a disturbing reflection on the display surface, the contour of the image is blurred and the screen image on the display can be easily recognized (the disturbing reflection is decreased). However, the light brownish looking of the display surface is sometimes strengthened to decrease the contrast in a bright room (bright-room contrast). Also, a device for increasing the light intensity of the backlight to enhance the visibility in a bright room, for example, a light-condensing member such as prism sheet, is being used.
In the case where a clear surface without antiglare property is used, a low refractive index layer having a low refractive index at a level enabling satisfactory reduction of disturbing reflection cannot be realized only by the antireflection utilizing thin-film interference of one low refractive index layer, and when thin-film interference by two or more layers differing in the refractive index is used, strong color tint and cost rise may be incurred.
Accordingly, a light-scattering film ensuring reduced disturbing reflection and enhanced bright-room contrast is being demanded. Also, a light-scattering film optimal for an image display device with a large screen and ensuring reduced disturbing reflection and enhanced bright-room contrast is being demanded.